Conventionally, “fluorescent dye-integrated nanoparticles” (50 to 300 nm) comprising a biorecognition molecule (e.g., a nucleotide, an antibody or biotin) have been known (for example, the paragraph [0035] of Patent Document 1). However, there has been offered no description with regard to a solution for the problems in genetic testing.
As probe reagents for FISH (Fluorescence in situ Hybridization), BAC probes in which a plurality of low-molecular-weight dyes are bound to a nucleic acid sequence called “BAC (Bacterial Artificial Chromosome) clone” are conventionally used (for example, the paragraph [0064] of Patent Document 2). For the preparation of such a BAC probe, nick-translation reaction is known as a method of binding the low-molecular-weight dyes and, in theory, the low-molecular-weight dyes can be bound to the sites of ¼ of the number of nucleic acid sequences of a BAC clone. However, since the binding of the low-molecular-weight dyes is limited to about ⅛ of the sites in the actual reaction, a further improvement in the sensitivity could not be expected in a genetic testing performed by a FISH method using a conventional BAC probe.
As described above, in order to obtain a strong fluorescence signal, a large number of low-molecular-weight dyes have to be bound; however, a necessary and sufficient number of low-molecular-weight dyes cannot be bound to a BAC clone having a short DNA sequence of, for example, about 5,000 bp and, therefore, probe reagents prepared from a BAC clone having a long DNA sequence of 80,000 to 1,000,000 bp have been used (Patent Document 3). Nevertheless, since such a long BAC clone is replicated in Escherichia coli cells and then extracted, there are problems in terms of preciseness, such as susceptibility to errors, lack of consistency in length and contamination with impurities and, when hybridization is performed with a probe reagent prepared from a long BAC clone obtained by such replication and subsequent extraction, there are cases where the probe reagent also non-specifically adsorbs to base sequences other than a specific gene.